1. Field of Invention
The invention relates to shaped fertilizers which may be in the form of powders, granules, but more specifically in the form of so-called fertilizer rods, and which contain plant nutrients together with a biocompatible and biodegradable thermoplastic binder. The invention is hereinbelow described substantially by way of the mixtures of valuable substances shaped as fertilizer rods while it is not restricted to this shape.
2. Discussion of Related Art
Fertilizer rods are employed in the home and garden area mainly for fertilizing pot plants. The fertilizer rods are stuck or pressed into the soil in order to provide the earth surrounding the plants with the required nutrients. Thereby it is possible to supply an easily and accurately metered amount of fertilizer. Also the release rate of the nutrient may be controlled by means of the amount of binder incorporated. Other marketing forms of such shaped fertilizers include pins, nails or wedges. For large area application of pre-determined nutrient mixtures having a controlled release rate, the marketing forms as initially mentioned of powders and/or granules may offer possibilities of an easy handling in practice.
With view to prior art, reference is made, for example, to DE-C2-32 29 954, DE-A1-32 47 917 and DE-C2-34 05 521 and to the additional pertinent material of prior art cited in these printed publications.
Fertilizer rods contain complex mixtures of inorganic and, optionally, organic components which are capable of providing the elements required for plant growth--either with some retardation or with direct onset of activity, according to one's choice. The elements to be taken into consideration include, more particularly, N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, Mo, B, Co, S and Na. Sustained-release nitrogen depot fertilizers have been selected, for example, from organic nitrogen compounds such as urea-formaldehyde condensate or crotonylidene-diurea, whereas ammonium, nitrate and amide nitrogen compounds are among the quick-acting constituents. Ammonium, potassium, magnesium and calcium phosphates that are soluble in water, ammonium nitrate and mineral acid have proven to be useful for supplying the plants with phosphate. Potassium is employed, for example, in the form of K.sub.2 SO.sub.4 or KCl, but potassium magnesium sulfate is also suitable. Magnesium may be employed in the form of various sulfate salts. Suitable further components of the mixtures are, for example, ammonium molybdate, zinc sulfate as well as boric acid. Suitable organic components that may be used as nutrients and/or as aggregates or fillers are peat, biomasses from bacteria and fungi, urea, horn shavings, horn meal, blood and bone meal, seaweed powder and the like. Also, further important constituents may further be plant-protective agents for reducing the undesired infestation of the plants with pests and/or pathogens. Further conventional aggregates to the agents of the type here involved are, for example, colorants and odorous substances, lubricants, inhibitors to urease and nitrification as well as quite simply fillers, for example sand.
The complex mixtures comprising the active substances of plant nutrients and plant-protective agents are intimately mixed with a thermoplastic binder which is usually water-soluble and, in this form, are shaped, for example into rods. The binder does not only serve the purpose of providing the complex mixture of the valuable materials with some stable form, but it may also affect the release characteristics of the respective shaped articles in practical use.
The binders hitherto employed--hereto cf. the literature cited in the introduction and the secondary literature mentioned therein--are synthetic or semi-synthetic polymer compounds, among which particular importance in practice is attached to polyethyleneglycol, polyvinyl pyrrolidone, carboxymethyl cellulose and, especially, polyvinyl alcohol.
It is the object of the teaching of the invention described hereinbelow, in substance mixtures of the type described here to employ a binder that has not been used hitherto. This binder is intended not only to be inexpensive and available in any desired amount, but it is also to provide all advantages in the manufacture of the shaped article, especially those having the shape of fertilizer rods. The dry forms of the final commercial material are to be sufficiently inert in the presence of the air and of the moisture present in the air under conditions of practice, so that any interferences with practical use, for example by that the material becomes tacky, undergoes changes in strength and the like, will not occur. Nevertheless, the invention wants to provide a binder which is not only biologically compatible, but which also can be designated as an additional valuable material itself.
The teaching according to the invention has been based on the observation that a thermomechanically digested and, thus, thermoplasticized starch is capable of satisfying this catalogue of a variety of objects.